The sinusoidal movement of C. elegans is generated by coordinated contraction and relaxation of the body wall muscles. This activity is controlled by excitatory, inhibitory and modulatory signals from the nervous system. We are interested in the role that the Rho GTPase pathway plays in this signaling. The
unc-73 gene encodes eight isoforms that contain up to two RhoGEF domains. In the nervous system the UNC-73 RhoGEF-1 domain specifically activates Rac GTPases in the process of axon guidance, while the RhoGEF-2 domain specifically activates Rho to influence neurotransmission (Steven et al, 1998, 2005).
unc-73 RhoGEF-2 domain mutants have a lethargic and egg-laying phenotype similar to Gaq pathway mutants and UNC-73E, a RhoGEF-2 isoform, is a Gaq (EGL-30) effector acting in parallel with PLCb (Williams et al, 2007). However, we have determined that activation of the Gas pathway suppresses the slow locomotion phenotype of the
unc-73 RhoGEF-2 domain mutants while the activated Gas pathway does not suppress the Gaq lethargic phenotype (Reynolds et al, 2005). Here we attempt to better define the role of the UNC-73 RhoGEF-2 isoforms in neurotransmission and their relationship with the Gaq and Gas pathways. UNC-73E expression in the cholinergic motor neurons fails to rescue the locomotion defects of RhoGEF-2 domain mutants. However, knocking out UNC-73 RhoGEF-2 isoforms in the cholinergic motor neurons by cell specific RNAi causes a decrease in locomotion rate and an unexpected coiler phenotype. To examine the functions of other genes in the cholinergic motor neurons, we expressed
egl-30,
unc-31, and
rho-1 RNAi constructs driven by the same
unc-17 cholinergic motor neuron promoter.
punc-17::
unc-31(RNAi) animals have a slow and coiled appearance similar to
punc-17::
unc-73(RNAi) animals. Our results suggest that UNC-73 plays an important role in the regulation of locomotion in the cholinergic motor neurons, and this regulation may involve the release of neuromodulators through UNC-31.
unc-73 RhoGEF-2 mutants do not show significant drug resistance in an aldicarb resistance assay, indicating that UNC-73 is unlikely to have a general role in neurotransmitter release. However, additional preliminary data from a coelomocyte uptake assay indicate neuropeptide release decreases in an
unc-73 RhoGEF-2 domain mutant, suggesting UNC-73 is involved in neuropeptide release. We are currently making double mutants to more closely examine the relationship between
unc-73 and the Gaq and Gas pathways. These studies will help determine the role of UNC-73 and Rho GTPase signaling in neurotransmission and the regulation of locomotion.